CN102384716A - Fixed wavelength absolute distance interferometer - Google Patents
Fixed wavelength absolute distance interferometer Download PDFInfo
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- CN102384716A CN102384716A CN2011103189685A CN201110318968A CN102384716A CN 102384716 A CN102384716 A CN 102384716A CN 2011103189685 A CN2011103189685 A CN 2011103189685A CN 201110318968 A CN201110318968 A CN 201110318968A CN 102384716 A CN102384716 A CN 102384716A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
- G01B9/02007—Two or more frequencies or sources used for interferometric measurement
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/026—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by measuring distance between sensor and object
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
- G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
- G01B9/02004—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using frequency scans
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02015—Interferometers characterised by the beam path configuration
- G01B9/02027—Two or more interferometric channels or interferometers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02041—Interferometers characterised by particular imaging or detection techniques
- G01B9/02048—Rough and fine measurement
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02055—Reduction or prevention of errors; Testing; Calibration
- G01B9/02062—Active error reduction, i.e. varying with time
- G01B9/02067—Active error reduction, i.e. varying with time by electronic control systems, i.e. using feedback acting on optics or light
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02097—Self-interferometers
- G01B9/02098—Shearing interferometers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
- G01B2290/45—Multiple detectors for detecting interferometer signals
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
- G01B2290/60—Reference interferometer, i.e. additional interferometer not interacting with object
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Abstract
Provided is a fixed wavelength absolute distance interferometer, including a first interferometer and a second interferometer. The first interferometer comprises a first light source transmitting a first light beam having a wavelength W toward a measurement target, a wavefront radius detector configured to provide a first measurement responsive to the wavefront radius at the wavefront radius detector, and a first path length calculating portion calculating a coarse resolution absolute path length measurement R. The second interferometer comprises a beam transmitting device transmitting a second-interferometer light beam having a wavelength [Lambda], a beam splitting/combining device separating the second-interferometer light beam into reference and measurement beams and combining the returning reference and measurement beams into a combined beam, a second-interferometer detector configured to receive the combined beam and provide signals of a phase of the combined beam, and a second path length calculating portion configured to determine a medium resolution absolute path length measurement ZM.
Description
Technical field
The present invention relates to a kind of fixed wave length absolute distance interferometer.
Background technology
In order to eliminate or to reduce to be included in through traditional (for example Michelson, Twyman-Green or Mach-Zehnder type) laser interferometer (U.S.7; 292; 347) error in the measurement result of measuring or fuzzy (ambiguity) have developed the absolute distance interferometer (ADI) that two laser frequencies are warbled.
In order to obtain the absolute distance of sample surfaces with high resolving power; In ADI, carry out coarse-medium-meticulous measurement scheme; Wherein bigness scale amount is used to eliminate 2 π phase ambiguities from medium measurement, and 2 π that medium measurement is used to eliminate from meticulous measurement then blur.
Above ADI can carry out inserting in the sub-wavelength (interpolation), on 1m or bigger potential absolute range, have nanometer resolution.
Summary of the invention
Yet there is shortcoming in some applications in top ADI, for example:
1, uses the frequency chirp of Δ λ=1nm, and, use the modulating frequency of 100Hz to be used to obtain coarse distance metric in order to adapt to limited detector bandwidth.As a result, measure sampling rate be restricted to low relatively value (＜100Hz).
2, the ADI system comprises outside cavity gas laser, so that frequency chirp to be provided, and adopts reference interferometer to calibrate wavelength chirp, and this has increased cost and complicacy to system.
In the interferometer structure (for example Michelson or Mach-Zehnder type) of traditional type, other known ADI utilize additional fixed wave length, rather than the wavelength of warbling, so that provide the absolute measurement range of usefulness.Yet, the lasing light emitter that this ADI typically need add, switchgear, calibrating installation etc.Therefore, the cost of this system and complicacy are not suitable for some application yet.
The purpose of this invention is to provide a kind of fixed wave length absolute distance interferometer; Said fixed wave length absolute distance interferometer has simple structure; And can eliminate to be included in from the wavelength in the measurement result of non-ADI and blur, so that on long relatively measurement range, accurate absolute distance measurement is provided economically.
First aspect of the present invention relates to a kind of fixed wave length absolute distance interferometer, comprising: first interferometer and second interferometer.First interferometer comprises: first light source; It comprises at least one first point source; Said at least one first point source has at least one first light beam of wavelength W towards the measurement target emission along the first interferometer measurement light path; The wherein said first interferometer measurement light path comprises the variable optical path length part with the length that changes along with the position of said measurement target, and said at least one first light beam has the wavefront radius that changes along with the distance of the said first interferometer measurement light path in edge; Wavefront radius detecting device; Be configured to provide first tolerance in response to the wavefront radius at said wavefront radius detecting device place; The said first interferometer measurement optical path length of the wherein said first tolerance indication; And first via electrical path length calculating section, be configured to coarse resolution absolute path length tolerance R based on the said first interferometer measurement optical path length of said first metric calculation.Second interferometer comprises: the light beam dispensing device, and sending provides synthetic second interferometer beam of measuring wavelength Λ; Beam separation/synthesizer; Said second interferometer beam is separated into reference beam and the measuring beam through the second interferometer measurement light path through fixed light path; And synthetic light beam is provided through the reference beam that will return from said fixed light path and the measuring beam that returns from said measurement target reflection and along the said second interferometer measurement light path are synthetic; Wherein, the said second interferometer measurement light path comprises the variable optical path length part with the length that changes along with the position of said measurement target; Second interferometric detector is configured to receive said synthetic light beam, and provide the indication with said synthetic light beam in the related phase place of synthetic measurement wavelength Λ
Signal; And the second path calculating section, be configured to based on number of wavelengths N by the indicated synthetic light beam of the signal of said second interferometric detector
Λ, wavelength Λ and phase place
Confirm the intermediate resolution absolute path length tolerance Z of the said second interferometer measurement optical path length
M, wherein: said number of wavelengths N
ΛBe the integer amount of calculating that is included in the complete wavelength Λ in the said second interferometer measurement optical path length, and based on said coarse resolution absolute path length tolerance R and and said first interferometer measurement optical path length and the said second interferometer measurement optical path length between constant difference C
12Relevant constant offset is calculated said number of wavelengths N
Λ
Description of drawings
Describe example embodiment of the present invention in detail according to following accompanying drawing, wherein:
Fig. 1 shows the synoptic diagram of structure of the fixed wave length absolute distance interferometer of first example embodiment;
Fig. 2 shows the synoptic diagram of structure of the fixed wave length absolute distance interferometer of second example embodiment;
Fig. 3 shows the synoptic diagram of structure of the fixed wave length absolute distance interferometer of the 3rd example embodiment;
Fig. 4 shows the synoptic diagram of structure of the fixed wave length absolute distance interferometer of the 4th example embodiment;
Fig. 5 shows the figure of the principle of coarse-medium-meticulous measurement of in the fixed wave length absolute distance interferometer of first to the 3rd example embodiment, using;
Fig. 6 shows the synoptic diagram of the structure of λ 2 detecting devices and λ 3 detecting devices in the fixed wave length absolute distance interferometer of first to the 3rd example embodiment; And
Fig. 7 is the synoptic diagram that is illustrated in the operation of λ 2 shown in Fig. 6 and λ 3 detecting devices.
Embodiment
1, first example embodiment
The fixed wave length absolute distance interferometer 1 of first example embodiment is described below.
As shown in Figure 1, fixed wave length absolute distance interferometer 1 comprises first interferometer 11 and the absolute optical path length tolerance of the intermediate resolution Z that is used to measure light path of the absolute optical path length tolerance of the coarse resolution that is used to measure light path (the first interferometer measurement light path) R
MWith the absolute optical path length tolerance of fine-resolution Z
F Second interferometer 12 of measurement.
Also link to each other (the not shown connection) with signal S3 from the signal S2 of λ 2 detecting devices 27 from λ 3 detecting devices 28 with computing machine 100.Computing machine 100 input signal S2 and S3, and the phase calculation intermediate resolution absolute growth tolerance Z of λ 3 component of signals of the synthetic light beam that detects according to the phase place of λ 2 component of signals of the synthetic light beam that detects through λ 2 detecting devices 27 and through λ 3 detecting devices 28
MWith fine-resolution absolute growth tolerance Z
F, and therefore also corresponding to the second path calculating section.Further describe intermediate resolution absolute growth tolerance Z as following
MWith fine-resolution absolute growth tolerance Z
FComprise the variable common path length part Z between mirror position M and the retroreflector 13
VCP, and the second interferometer constant path portion C
2, the second interferometer constant path portion C
2For example comprise come since mirror position M to the approximate path part BM that limits of the separation/synthesising position B of beam separation/synthesizer 25 and approximate from separations/synthesising position B to detector location D ' path of the path part BD of (or D ") contribute.
In Fig. 6 and 7, show in detail around beam separation/synthesizer 25, reference mirror 26, the structure of second interferometer 12 of λ 2 detecting devices 27 and λ 3 detecting devices 28, and show the structure of an embodiment of λ 2 detecting devices 27 and λ 3 detecting devices 28 especially.In each embodiment, λ 2 detecting devices 27 can have and the identical structure of λ 3 detecting devices 28, but are appreciated that other known quadrature (quadrature) signal detecting methods also can be used for arbitrary detecting device in the embodiment that substitutes.
Shown in Fig. 1 and 6, on the light path of second interferometer beam that gets into beam separation/synthesizer 25, half-wave plate 251 is set, so that separable reference beam and measuring beam component to be provided.On the measuring beam exit facet and reference beam exit facet of beam separation/synthesizer 25, quarter- wave plate 252 and 253 are provided respectively, so that when they are back to beam separation/synthesizer 25, right transmission and reflection are provided to light beam.Through the measuring beam exit facet of beam separation/synthesizer 25, measuring beam goes out to inject the second interferometer measurement light path, and through the reference beam exit facet of beam separation/synthesizer 25, reference beam is towards reference mirror 26 outgoing simultaneously.
On the light path of the synthetic light beam of exporting through beam separation/synthesizer 25; Beam splitting mean 254 will be λ 2 component of signals parts from the synthetic beam separation of beam separation/synthesizer 25 with λ 3 component of signals partly (for example; Through comprising the wave length filtering interface; Be used for λ 2 wavelength are guided to λ 2 detecting devices 27, and λ 3 wavelength are guided to λ 3 detecting devices 28).
In the embodiment shown in Fig. 6 and Fig. 7, λ 3 detecting devices 28 comprise: Polarization-Sensitive beam deflection element (PSBDE) 256, and it partly is separated into not deflected beam and the deflected beam that has been deflected angle of divergence θ with λ 3 component of signals; Mix polarizer 257, it is oriented at deflection and the halfway (half way) between the polarization angle of deflected beam not; And photodetector array 225, it detects the interference fringe of interfering generation by the result between deflected beam and the deflected beam not.PSBDE 256 has at U.S.7, and the PSBDE structure of describing in 333,214 all merges to its disclosed content here by reference.U.S.7; 333; 214 patents disclose and second interferometer, 12 similar interferometers; And a kind of method is disclosed, the method for reference that is used for utilizing PSBDE to import cross polarization and target (measurement) light beam (such as appearing at those of λ 3 (or λ 2) component of signal part), and generate have with reference and target (measurement) light beam between the interference fringe 145 that differs relevant variable position (space phase); Be used to utilize photodetector array to indicate the variable spaces phase place of striped 145; And be used for calculating differing between reference and the measuring beam of cross polarization according to indicated space phase.According to known interferometer principle, the variation of the path of measuring beam is represented in the variation that differs.
In certain embodiments, for along variable common path length part Z
VCPAim at the light beam of first and second interferometers; Do not crosstalk and between them, do not introduce, dichronic mirror 29 is set to along the second interferometer measurement light path, and on the first interferometer measurement light path; And work passes through the light beam with wavelength X 1, and reflection has the light beam of non-λ 1 wavelength simultaneously.
Rubidium unit (rubidium cell) 31 (or other references) can provide calibration reference, and to guarantee the stability of wavelength X 2 and λ 3, said wavelength can be corresponding to the absorbing wavelength of rubidium unit 31.Rubidium unit 31 can receiving beam synthesizer 23 places the part of second interferometer beam of output.λ 2 absorption detectors 32 can detect λ 2 parts in second interferometer beam of passing rubidium unit 31, and λ 3 absorption detectors 33 can detect λ 3 parts in second interferometer beam of passing rubidium unit 31.Can dispose absorption detector 32 and 33 according to known method; So that when second generating laser 21 and the 3rd generating laser 22 are tuned to suitable wavelengths λ 2 with λ 3 respectively; The power that senses λ 2 parts and λ 3 parts in second interferometer beam of passing rubidium unit 31 descends, and absorption detector 32 and 33 can be exported the appropriate control signal and controls this result of generating laser realization.
The operation of fixed wave length absolute distance interferometer 1 is described below.
In first interferometer 11, carry out the coarse resolution measurement of measuring optical path length through following processes.At first, 14 emissions of first generating laser have the laser beam of wavelength X 1 (for example 633nm).Then, be focused the optical fiber 17, and transmit, and be transmitted in the beam splitting mean 15 as point source in the end of optical fiber 17 through optical fiber 17 from first generating laser, 14 emitted laser bundles.Beam splitting mean 15 separates into two laser beam with laser beam, and it shows as from two point sources.Two laser beam have the wavelength of λ 1, and therefore pass dichroic filters 29, and towards retroreflector 13 transmission, retroreflector 13 provides movably measurement target.Because close to each other from two laser beam of retroreflector 13 reflections, so they interfere with each other to generate interference fringe.
Imaging array 19 detects by these two interference fringes that light beam forms, and therefore wavefront radius detecting device 16 is provided, as follows.COMPUTER CALCULATION is by the spacing P of imaging array 19 detected interference fringes, and then through the absolute optical path length tolerance of the coarse resolution of following equation (1) acquisition R, it is roughly identical with the wavefront radius:
R＝(c*ls*P)/λ1 (1)
Wherein P is the spacing (or between distance) of interference fringe maximum value, and c depends on the geometric factor of two point sources with respect to the aligning of the detection plane of interference fringe pattern, and ls is the distance between two point sources in beam splitting mean 15 places.According to equation (2), the absolute optical path length tolerance of coarse resolution R is corresponding to the variable common path measuring distance Z of previous general introduction
VCPWith the first interferometer constant path portion C
1:
R＝(2*Z
VCP)+C
1(2)
In second interferometer 12, carry out the absolute optical path length tolerance of intermediate resolution Z through following step
MWith the absolute optical path length tolerance of fine-resolution Z
FFrom the emission of second generating laser 21 and have λ 2 light beams of wavelength X 2 (for example 780nm) and be imported into the beam synthesizing device 23 from 22 emissions of the 3rd generating laser and λ 3 light beams with wavelength X 3 (for example 795nm).At beam synthesizing device 23 places, λ 2 light beams and λ 3 light beams are synthetic, and to generate second interferometer beam, this second interferometer beam comprises two wavelength and synthetic wavelength Λ is provided:
Λ＝λ2*λ3/|λ3-λ2|(3)
Get into beam separation/synthesizer 25 from the approximate entire portion of beam synthesizing device 23 transmission second interferometer beam through half-wave plate 251, so that be divided into measuring beam and reference beam.The polarization of half-wave plate 251 rotations second interferometer beam, thus make beam separation/synthesizer 25 that the measurement and the reference beam of the cross polarization with similar intensity are provided.
Part from second interferometer beam of beam synthesizing device 23 sees through rubidium unit 31, and by λ 2 detecting devices 32 and 33 monitoring of λ 3 detecting devices, as stated.
Measuring beam is input to light beam separation/synthesizer 25, and through second interferometer measurement optic path to the retroreflector 13.Along the second interferometer measurement light path, measuring beam passes quarter-wave plate 252, and by dichroic filters 29 reflections.Measuring beam by retroreflector 13 reflections is back to quarter-wave plate 252 and beam separation/synthesizer 25 through the second interferometer measurement light path.Through quarter-wave plate 252 and its polarization, so that it passes light beam separation/synthesizer 25 when returning along the reflection modification measuring beam of the second interferometer measurement light path.
Simultaneously, the reference path that reference beam passes light beam separation/synthesizer 25, quarter-wave plate 253 and has regular length by reference mirror 26 reflection, and is back to and has the beam separation/synthesizer 25 that makes its polarization that is reflected.
It is synthetic light beam that measuring beam and the reference beam that is back to beam separation/synthesizer 25 is synthesized at beam separation/synthesizer 25 places, and is transferred in the beam splitting mean 254.At beam splitting mean 254 places, synthetic light beam is separated into λ 2 component of signals part and λ 3 component of signals part (for example through the wave length filtering interface in the beam splitting mean 254).
Then, through following equation (5), with the absolute light path linear measure longimetry of intermediate resolution Z
MWith phase place
Related:
N wherein
ΛBe the quantity of whole synthetic wavelength in the second interferometer measurement light path (having wavelength Λ).
In addition, according to equation (6), Z
MWith aforesaid variable common path measuring distance Z
VCPWith the second interferometer constant path portion C
2Relevant:
Z
M＝(2*Z
VCP)+C
2 (6)
According to equation (6) and (2):
Z
M＝R-C
1+C
2 (7)
We can definition amount C
12=(C
1-C
2), it can be considered to the constant path length difference between the measurement light path of first and second interferometers.Can know C through design or test
12According to equation (5) and (7):
N
Λ=| R-C
12| the integral part of/Λ (7)
Because through first interferometer 11 measure R utterly, like top general introduction, so can confirm N according to this measurement
Λ, and according to measuring and equation (7), the combination of (4) and (5) can be confirmed Z with the improvement precision with respect to R
M
When retroreflector 13 is mobile with respect to imaging array 19 (wavelength radius detecting device 16), shown in accompanying drawing, like the quantity N of top general introduction ground calculating ripple
ΛYet, also can have such embodiment: wherein with the retroreflector components identical on assembling wavelength radius detecting device 16, thereby the first interferometer measurement light path only strides across common path length part Z
VCPOnce, and arrive wavelength radius detecting device 16, and:
R＝Z
VCP+C’
1 (8)
C ' wherein
1Be the constant path part related with the first such interferometer measurement optical path length.
When with respect to wavefront radius detecting device 16 fixedly during retroreflector 13, the quantity N through following Equation for Calculating ripple then
Λ:
N
Λ=| 2R-C '
12| the integral part of/Λ (9)
(C ' wherein
12Be that the such first interferometer measurement optical path length and constant between the second interferometer measurement optical path length is poor, C ' for example
12=2C '
1-C
2).
In addition, according to the absolute optical path length tolerance of the intermediate resolution that obtains through top process Z
M, COMPUTER CALCULATION number of wavelengths N
λ i, N
λ iBe the absolute optical path length tolerance of intermediate resolution Z
MThe quantity of the wavelength X i of middle λ i light beam (i=2 or 3), and be through the absolute optical path length of intermediate resolution is measured Z
MThe merchant's who obtains divided by wavelength X i integral part, and then through following equation (10), based on the number of wavelengths N that obtains
λ iPhase place with the λ i light beam that detects through λ i detecting device
Calculate the absolute optical path length tolerance of fine-resolution Z
F:
Wherein, C
IFMBe through tolerance Z
FThe path of tolerance and tolerance Z
MPoor between the path of tolerance, and be the constant with the location independent of retroreflector 13 (measurement target).
At coarse resolution tolerance R, intermediate resolution tolerance Z shown in Fig. 5
MWith fine resolution rate metric Z
FBetween relation.Suppose that wavelength X 1, λ 2 and λ 3 are respectively 633nm, 780nm and 795nm, and coarse resolution tolerance R=123.42nm.
Shown in Fig. 5, for example for the type of first interferometer disclosed herein, coarse resolution tolerance comprises coarse error, and it is less than synthetic wavelength, and can be 10 microns the order of magnitude.Therefore, coarse resolution tolerance is for confirming N
ΛReliable basis is provided, and according to N
Λ, second interferometer beam synthetic wavelength Λ (42 μ m (=λ 2* λ 3/| λ 3-λ 2|)), with and phase place
Carry out intermediate resolution tolerance Z
MCalculating.Phase place
Measuring error can be less than wavelength X 2 or λ 3 be significantly smaller than coarse error and be enough to confirm reliably N so that provide
λ iThe medium range error.In described example, intermediate resolution tolerance Z
MGreater than coarse resolution tolerance R 0.0037mm.That is intermediate resolution tolerance Z,
MBe 123.4237mm.
According to wavelength X 2 or λ 3 and phase place
Or
Carry out fine resolution rate metric M
FCalculating so that reduce the medium range error.In described example, when according to N
λ 3, wavelength X 3 (=795nm) and phase place
Calculate fine resolution rate metric M
FThe time, fine resolution rate metric M
FLess than intermediate resolution tolerance Z
M0.000028mm, i.e. fine resolution rate metric M
FBe 123.423672mm (123.4237mm-0.000028mm).
The structure of first interferometer 11 be confirmed as make its have scope with two fixed wave length second interferometer 12 desired combination to resolution than (or scope is to ratio of precision).Previous also not to be familiar with or to adopt the desirable essence of this combination in this disclosed mode.In the fixed wave length absolute distance interferometer of first example embodiment, laser with fixed wavelength can be used as first, second and the 3rd generating laser.Therefore the use that can omit outside cavity gas laser, in addition, first interferometer 11 and second interferometer 12 are vibrated the influence with drift error lessly, and have improved fiduciary level.
In addition, in first interferometer 11, do not adopt warbling of specific modulation frequency (for example 100Hz), to obtain coarse resolution tolerance R.Therefore, data bandwidth be not limited to low relatively value (＜100Hz).
In addition, first interferometer 11 and second interferometer 12 all have than U.S.7, the structure much simple in structure of 292,347 ADI.
Substitute beam splitting mean 15; Can adopt two point light source by first optical fiber and second fiber configuration; Wherein, introduce laser beam from first generating laser 14 from an end of this first optical fiber, and first fiber configuration, first point source; And introduce laser beam from an end of this second optical fiber, and second fiber configuration is positioned near second point source of first point source from first generating laser 14.Second optical fiber can be from first optical fiber along separate routes.Also can be through close to each other and towards two generating lasers configuration two point light sources of retroreflector 13 emission of lasering beam.
2, second example embodiment
The fixed wave length absolute distance interferometer 2 of second example embodiment is described below.
Shown in Fig. 2, fixed wave length absolute distance interferometer 2 comprises first interferometer 11 and second interferometer 12.Second interferometer 12 has the structure identical with second interferometer 12 of the fixed wave length absolute distance interferometer 1 of first example embodiment.
The structure of first interferometer 11 is described below.Shown in figure 2 among the embodiment of first interferometer 11, wavefront radius detecting device 16 ' comprise wedge-shaped element 18, and utilize lateral shear (shearing) the wavefront radius of known type to detect, and can omit beam splitting mean 15.Wedge-shaped element 18 is the clapboards that formed by transparent material, and is configured to make and runs into front surface FS from first generating laser, 14 emitted laser bundles and tilt at incident angle θ, for example 45 degree.At the back surperficial BS that arranges wedge-shaped element 18 about the angle of wedge Δ θ place of front surface FS.
From first generating laser, 14 emitted laser bundles transmission through optical fiber 17, and from the point source aperture 17A of the end of optical fiber 17 to retroreflector 13 transmission.
First interferometer beam bump wedge-shaped element 18 that returns, and produce two wavefront that reflect through its front surface FS and surperficial thereafter BS respectively, thus make them can interfere and form interference fringe.Wavefront radius detecting device 16 ' be positioned and be configured so that it receives the interference fringe that forms, said interference fringe is detected by imaging array 19.
Except above-described structural difference, first interferometer 11 of fixed wave length absolute distance interferometer 2 has the identical structure of first interferometer with the fixed wave length absolute distance interferometer of first example embodiment.
The function of fixed wave length absolute distance interferometer 2 is described below.
In first interferometer 11, because point source aperture 17A is single point source, so have before single spherical wave the laser beam with wavelength X 1 by first generating laser, 14 emitted laser Shu Zuowei from point source aperture 17A emission.
Single wavefront laser beam is walked around (bypass) wedge-shaped element 18, and passes dichroic filters 29,13 transmission along the first interferometer measurement path towards retroreflector, and by retroreflector 13 reflected backs.Single wavefront of the laser beam of returning is split into two approximately uniform wavefront with approximately equalised radius-of-curvature at wedge-shaped element 18 places, then, reflect two wavefront by wedge-shaped element 18 towards imaging array 19.Imaging array 19 detects the interference fringe that is formed by two wavefront.Because the thickness and the angle of wedge Δ θ of wedge-shaped element 18, two wavefront are along separated shear distance of shear plane direction or side-play amount LS.The LS value is can be by design or the definite constant of experiment.As known usually for this clapboard, because the work of wedge-shaped element 18, the striped that generates before the spherical wave is rotated in angle γ place about shear plane (or about angle related with plane wave front).COMPUTER CALCULATION is by the spacing and the angle of the interference fringe of imaging array 19 detections.According to following equation, the angle γ of the interference fringe that detects through spacing P and imaging array 19 according to interference fringe obtains coarse resolution by the computing machine that links to each other with imaging array 19 and measures R (it is the wavefront radius R):
R＝LS*P/(λ1*sinγ)(11)
In certain embodiments, computing machine can utilize the Fourier analysis technology to confirm spacing P and angle γ.In certain embodiments; The structure of clapboard element and relevant detection can for example be similar to as described in the following article: Mehta etc.; " Distance Measurement with Extended Range using Lateral Shearing Interferometry and Fourier Transform Fringe Analysis "; Optical Engineering, in June, 2005.Described in the document, also can use plate configuration wavefront radius detecting device with parallel surfaces rather than angle of wedge.Therefore, above-mentioned clapboard structure only is an example, and is not restrictive.
With with the same way as described in first example embodiment, second interferometer 12 carries out work, and carries out intermediate resolution tolerance Z
MWith fine resolution rate metric Z
FCalculating.
As described above, single wavefront of 17A emitted laser bundle is not separated into two wavefront from the point source aperture, but before generating second wavefront, advances through the whole first interferometer measurement path.Therefore; The interference fringe distortion that obtains is littler, therefore, compares with the fixed wave length absolute distance interferometer with first interferometer that comprises the two point light source; Even under the condition that disturbance is not more controlled by strictness, first interferometer 11 also has the robustness (robustness) and the precision of raising.
3, the 3rd example embodiment
The fixed wave length absolute distance interferometer 3 of the 3rd example embodiment is described below.
In the embodiment of first interferometer 11 shown in Fig. 3, use wavefront radius detecting device 16 " replacement wavefront radius detecting device 16 '.Wavefront radius detecting device 16 " utilize the lateral shear wavefront radius of known type to detect; and to comprise reflecting element RE, first polarizer+45P, Savart plate (Savart Plate) SP, second polarizer-45P and imaging array 19, they such as descriptions of following further institute work.
Except difference recited above, fixed wave length absolute distance interferometer 3 can have structure and the operation identical with the fixed wave length absolute distance interferometer of second example embodiment 2.
The function of fixed wave length absolute distance interferometer 3 is described below.
From first laser instrument, 14 emitted laser bundles transmission through optical fiber 17, and from the point source aperture 17A of the end of optical fiber 17 to retroreflector 13 transmission.Single wavefront laser beam is walked around reflecting element 18, and passes dichroic filters 29 along the first interferometer measurement path towards retroreflector 13, and by retroreflector 13 reflected backs.Reflect first interferometer beam of returning by reflecting element 18, and pass first polarizer+45P to Savart plate SP.According to the known work principle of Savart plate SP, single wavefront of the laser beam of returning is split into two approximately uniform wavefront, and they have approximately uniform radius-of-curvature and perpendicular to their the side-play amount ls of the direction of propagation.The ls value is and the related constant of design that can be designed or test definite Savart plate.Then, two wavefront transmission make them interfere through second polarizer-45P, and towards imaging array 19.Imaging array 19 detects the interference fringe that is formed by two wavefront.Computing machine 100 can calculate the spacing of the interference fringe that is detected by imaging array 19.The spacing P of the interference fringe that detects based on imaging array 19, the computing machine that links to each other with imaging array 19 can obtain coarse resolution according to the same analysis described in first example embodiment and measure R.In certain embodiments; Wavefront radius detecting device 16 " structure and coherent detection can be similar to such as for example following document description: Haulser etc.; " Range Sensing Based on Shearing Interferometry ", Applied Optics, in November, 1988.
4, the 4th example embodiment
The fixed wave length absolute distance interferometer 4 of the 4th example embodiment is described below.
As shown in Figure 4, fixed wave length absolute distance interferometer 4 comprises first interferometer 11 and second interferometer 12 with following structure.
In the embodiment shown in Fig. 4; Fixed wave length absolute distance interferometer 4 comprises: beam splitting mean 24, said beam splitting mean 24 are arranged the part of separating and seeing through from the light of second generating laser 21 and get into optical fiber 17 to be used to first interferometer 11; Optical gate (shutter) element 36 is configured to block off and on second interferometer beam; And traditional beam splitter 35 (for example partially silvered mirror), substitute first, second with the 3rd example embodiment in the dichroic filters 29 used.Also can optionally comprise spatial filter arrangement 38.Utilize this structure, can use two generating lasers rather than three, as be described in more detail below.
Except above-described structure, fixed wave length absolute distance interferometer 4 can have structure and the approximately uniform measuring method identical with the fixed wave length absolute distance interferometer of second example embodiment 2.
The function of fixed wave length absolute distance interferometer 4 is described below.
Because identical wavelength X 2 is used in first interferometer 11 and second interferometer 12; Optical gate element 36 can be used to suspend the operation of second interferometer 12; Thereby when definite signal S1, the signal S1 in first interferometer 11 is not disturbed by λ 2 light beams from second interferometer 12.Computing machine 100 can be exported optical gate control signal Cs, so that close optical gate element 36 in the suitable time for this purpose, and opens optical gate element 36 then again to confirm signal S2 and S3.Owing to disperse from its point source from λ 2 light beams of first interferometer 11, thus its a little less than than 2 light beams of the λ in second interferometer many, therefore during the signal S2 in confirming second interferometer 12, need not suspend the operation of first interferometer 11.In addition, in certain embodiments, can use heart spatial filter arrangement 38 far away as illustrated in fig. 4.As known for heart spatial filter arrangement far away (such as, spatial filter arrangement 38), the light of having blocked collimation not basically or having dispersed through this device.Therefore, stoped diverging light to arrive second interferometer 12 basically from first interferometer 11.
In fixed wave length absolute distance interferometer 4, can omit first generating laser 14, therefore, to compare with the fixed wave length absolute distance interferometer of second example embodiment, its structure can be simpler.
The front of example embodiment of the present invention is described and has been provided for the purpose of describing and illustrating.Do not attempt limit or limit the invention to disclosed precise forms.For example; Although the length item with in the previous openly equation has defined the optical path difference between first and second interferometers; Person of skill in the art will appreciate that, in each embodiment, can utilize more general " skew " constant that uses in the similar compatible equation with the consistent term of other mathematics (such as wavelength or phase place etc.) definition; Comprise the constant path length difference, other constant factors etc.Significantly, a plurality of modifications and modification will be obvious to those skilled in the art.Select and the description example embodiment, so that explain principle of the present invention and its practical application, the various modifications that therefore allow others skilled in the art to understand various embodiment of the present invention and be applicable to the concrete purposes of being conceived best.Be intended to limit scope of the present invention through following claim and their equivalent.
Claims (20)
1. fixed wave length absolute distance interferometer comprises:
First interferometer comprises:
First light source; It comprises at least one first point source; Said at least one first point source has at least one first light beam of wavelength W towards the measurement target emission along the first interferometer measurement light path; The wherein said first interferometer measurement light path comprises the variable optical path length part with the length that changes along with the position of said measurement target, and said at least one first light beam has the wavefront radius that changes along with the distance of the said first interferometer measurement light path in edge
Wavefront radius detecting device is configured to provide first tolerance in response to the wavefront radius at said wavefront radius detecting device place, the said first interferometer measurement optical path length of the wherein said first tolerance indication, and
First via electrical path length calculating section is configured to the coarse resolution absolute path length tolerance R based on the said first interferometer measurement optical path length of said first metric calculation; And
Second interferometer comprises:
The light beam dispensing device, sending provides synthetic second interferometer beam of measuring wavelength Λ,
Beam separation/synthesizer; Said second interferometer beam is separated into reference beam and the measuring beam by the second interferometer measurement light path by fixed light path; And synthetic light beam is provided by the reference beam that will return from said fixed light path and the measuring beam that returns from said measurement target reflection and along the said second interferometer measurement light path are synthetic; Wherein, The said second interferometer measurement light path comprises the variable optical path length part with the length that changes along with the position of said measurement target
Second interferometric detector; Be configured to receive said synthetic light beam; And the signal of the related phase place
of synthetic measurement wavelength Λ in indication and the said synthetic light beam is provided, and
The second path calculating section is configured to based on the number of wavelengths N by the indicated synthetic light beam of the signal of said second interferometric detector
Λ, wavelength Λ and phase place
Confirm the intermediate resolution absolute path length tolerance Z of the said second interferometer measurement optical path length
M, wherein:
Said number of wavelengths N
ΛBe the integer amount of calculating that is included in the complete wavelength Λ in the said second interferometer measurement optical path length, and
Based on said coarse resolution absolute path length tolerance R and and said first interferometer measurement optical path length and the said second interferometer measurement optical path length between constant difference C
12Relevant constant offset is calculated said number of wavelengths N
Λ
2. fixed wave length absolute distance interferometer as claimed in claim 1; Wherein wavefront radius detecting device is configured to detect the interference fringe pattern that is formed by said first light beam and second light beam; Said second light beam have wavelength W and with the similar wavefront radius of the wavefront radius of said first light beam, and at least near said wavefront radius detecting device place and said first beam interference.
3. fixed wave length absolute distance interferometer as claimed in claim 2, wherein said wavefront radius detecting device comprise that lateral shear arranges, said lateral shear is arranged from said first light beam provides said second light beam near the copy of said wavefront radius detecting device.
4. fixed wave length absolute distance interferometer as claimed in claim 3, wherein said lateral shear are arranged and are comprised Savart plate.
5. fixed wave length absolute distance interferometer as claimed in claim 2, wherein said wavefront radius detecting device comprises imaging array.
6. fixed wave length absolute distance interferometer as claimed in claim 2; Wherein in the first via electrical path length calculating section of said first interferometer; The fringe spacing P of the interference fringe pattern that detects based on said wavefront radius detecting device, the wavelength W of said first and second light beams and perpendicular to the separating distance ls of the parallel radius measurement of said first and second Beam Wave-Front calculate the coarse resolution absolute path length tolerance R of said measurement light path.
7. fixed wave length absolute distance interferometer as claimed in claim 6, wherein measure R through the coarse resolution absolute path length of the said measurement light path of following equation (1) calculating:
R＝(c*ls*P)/λ1 (1)
Wherein c depends on the factor of said parallel radius with respect to the aligning of the detection plane of said interference fringe pattern.
8. fixed wave length absolute distance interferometer as claimed in claim 2; Wherein said first light source comprises second point source near said first point source; And said second point source sends said second light beam along the said first interferometer measurement light path towards said measurement target, and wherein said second light beam has the wavefront radius that changes along with the distance of the said first interferometer measurement light path in edge.
9. fixed wave length absolute distance interferometer as claimed in claim 8, wherein said first light source comprises:
Optical transmitting set is launched the light with said first wavelength W through said first point source, so that said first light beam to be provided; And
Beam splitting mean, near said first point source, and part transmission and said first light beam of partial reflection, so that first light beam of partial reflection provides second point source that sends said second light beam.
10. fixed wave length absolute distance interferometer as claimed in claim 8, wherein said first light source comprises:
First optical fiber has the end that said first point source is provided;
Second optical fiber has the end that said second point source is provided; And
Optical transmitting set, emission has the light of the said first wavelength W, and the light of wherein being launched is coupled to said first and second optical fiber among both.
11. fixed wave length absolute distance interferometer as claimed in claim 1, wherein:
The light beam dispensing device of said second interferometer comprises:
Secondary light source, λ 2 light beams that emission has wavelength X 2;
The 3rd light source, λ 3 light beams that emission has the wavelength X 3 that is different from said wavelength X 2; And
Beam synthesizing device synthesizes second interferometer beam that said synthetic measurement wavelength Λ is provided with said λ 2 light beams and said λ 3 light beams, wherein provides said wavelength Λ through equation Λ=λ 2* λ 3| λ 3-λ 2|,
Said second interferometric detector comprises:
λ 2 detecting devices, detect the measuring beam component of λ 2 light beams in the said synthetic light beam with respect to the phase place
of reference beam component and
λ 3 detecting devices, detect the measuring beam component of λ 3 light beams in the said synthetic light beam with respect to the phase place
of reference beam component and
In the said second path calculating section; Through following equation (2), the phase place
that phase place
that detects based on said λ 2 detecting devices and said λ 3 detecting devices detect obtain with said synthetic light beam in the related phase place
of synthetic measurement wavelength Λ
12. fixed wave length absolute distance interferometer as claimed in claim 11, the wherein said second path calculating section is confirmed said intermediate resolution absolute path length tolerance Z through following equation (3)
M:
13. fixed wave length absolute distance interferometer as claimed in claim 12 is configured according to one of following structure:
Structure (a), wherein said wavefront radius detecting device are arranged such that said measurement target moves with respect to said wavefront radius detecting device, and the said second path computing section number of wavelengths N
Λ, so that it is equivalent to amount [R-C
12] merchant's that obtains divided by wavelength Λ integral part, and
Structure (b), wherein said wavefront radius detecting device are arranged such that said measurement target fixes with respect to said wavefront radius detecting device, and the said second path computing section number of wavelengths N
Λ, so that it is equivalent to amount [2R-C
12] merchant's that obtains divided by wavelength Λ integral part.
14. fixed wave length absolute distance interferometer as claimed in claim 11, the said intermediate resolution absolute path of wherein said second path computing section length tolerance Z
M, calculate number of wavelengths N then
λ i, number of wavelengths N
λ iBe said intermediate resolution absolute path length tolerance Z
MThe quantity of the wavelength X i of middle λ i light beam, wherein i=2 or 3, and number of wavelengths N
λ iBe with said intermediate resolution absolute path length tolerance Z
MThe merchant's who obtains divided by wavelength X i integral part, then, the said second path calculating section is based on the number of wavelengths N that is obtained
λ iAnd the phase place of the λ i light beam of said λ i detecting device detection
Calculate fine-resolution absolute path length tolerance Z
F
15. fixed wave length absolute distance interferometer as claimed in claim 14, the wherein said second path calculating section is confirmed said fine-resolution absolute path length tolerance Z through following equation (4)
F:
Wherein, Ci
FMBe tolerance Z
FThe path of tolerance and tolerance Z
MPoor between the path of tolerance, and be the constant with the location independent of said measurement target.
16. fixed wave length absolute distance interferometer as claimed in claim 1, wherein:
The light beam dispensing device of said second interferometer comprises:
Secondary light source, λ 2 light beams that emission has wavelength X 2,
The 3rd light source, λ 3 light beams that emission has the wavelength X 3 that is different from said wavelength X 2, and
Beam synthesizing device synthesizes second interferometer beam that said synthetic measurement wavelength Λ is provided with said λ 2 light beams and said λ 3 light beams;
Said fixed wave length absolute distance interferometer also comprises the measuring beam inflector assembly; And
Said fixed wave length absolute distance interferometer is configured to make:
The deflection of said measuring beam inflector assembly is included at least some light among in (a) said at least one first light beam and (b) the said measuring beam; Thereby before above-mentioned light arrives said measurement target; It becomes and said variable optical path length section aligned, and
The transmission of said measuring beam inflector assembly is included at least some light in (a) said at least one first light beam and (b) the said measuring beam another; Thereby before above-mentioned light arrived said measurement target, it kept and said variable optical path length section aligned.
17. fixed wave length absolute distance interferometer as claimed in claim 16, wherein:
Wavelength W is different from wavelength X 2 and λ 3;
Said measuring beam inflector assembly comprises dichroic filters, and said dichroic filters transmission has the light of wavelength W, but reflection has the light of wavelength X 2 or λ 3; And
Said dichroic filters is arranged to the said measuring beam of reflection; Make said measuring beam arrive before the said measurement target; Become and said variable optical path length section aligned; And arrive said measurement target and by after said variable optical path length partial reflection is returned at said measuring beam, said measuring beam is reflected into makes it aim at said beam separation/synthesizer.
18. fixed wave length absolute distance interferometer as claimed in claim 16, wherein:
Wavelength W is identical with one of λ 3 with wavelength X 2; And
Said fixed wave length absolute distance interferometer also comprises optical gate; Said optical gate was arranged and is controlled to be during the wavefront radius sensors work time period of said first interferometer, stoped the measuring beam of said second interferometer to arrive said measuring beam inflector assembly.
19. fixed wave length absolute distance interferometer as claimed in claim 18 is configured to make the optical transmitting set of a wavelength providing identical with W among wavelength X 2 and the λ 3 also to first light source of said first interferometer light to be provided.
20. interferometer measuring system as claimed in claim 1, wherein all light beams are by forming from the light of laser instrument emission.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US12/854,784 | 2010-08-11 | ||
| US12/854,784 US8179534B2 (en) | 2010-08-11 | 2010-08-11 | Fixed wavelength absolute distance interferometer |
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| CN102384716A true CN102384716A (en) | 2012-03-21 |
| CN102384716B CN102384716B (en) | 2016-02-03 |
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| US (1) | US8179534B2 (en) |
| EP (1) | EP2418456B1 (en) |
| JP (1) | JP2012037514A (en) |
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| Publication number | Publication date |
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| CN102384716B (en) | 2016-02-03 |
| JP2012037514A (en) | 2012-02-23 |
| EP2418456B1 (en) | 2013-03-27 |
| EP2418456A1 (en) | 2012-02-15 |
| US20120038930A1 (en) | 2012-02-16 |
| US8179534B2 (en) | 2012-05-15 |
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